A power converter transforms an input voltage into a regulated output voltage and supplies a current required by an external load such as integrated circuits and the like. Depending on whether a transformer is incorporated into a power converter, switching power converters can be divided into two categories, namely isolated power converters and non-isolated power converters. Isolated power converters can be implemented by using different power topologies, such as flyback converters, forward converters, half bridge converters, full bridge converters, push-pull converters, inductor-inductor-capacitor (LLC) resonant converters and the like. Likewise, non-isolated power converters can be implemented by using different power topologies such as buck converters, boost converters, buck-boost converters, linear regulators, any combinations thereof.
As the demand for battery based power applications has grown recently, there has grown a need for developing a converter capable of generating a regulated output voltage from an input voltage, which may be larger than, equal to, or smaller than the output voltage. For example, in a battery based power application, when a battery is fresh, it may supply a voltage higher than the output voltage of the converter. On the other hand, when the battery is depleted, it may supply a voltage lower than the output voltage of the converter.
Buck-boost converters have emerged as an effective power conversion scheme to deliver a tightly regulated output voltage from a wide range input voltage. A buck-boost converter can produce an output voltage that is either greater than or less than an input voltage through using different operating modes such as buck and boost conversion modes. In particular, the buck-boost converter operates in a buck mode when the input voltage is higher than the output voltage, in a boost mode when the input voltage is lower than the output voltage.